Chronic infectious and inflammatory diseases of humans are a significant public health challenge worldwide and greater understanding the human immune system will be essential in the design of new therapies to target these conditions. While significant advances have been made in defining the development and function of the murine immune system, a lack of access to non-diseased human tissue samples has hampered our progress in defining the phenotype and functional potential of immune cells isolated from different human tissue sites. Elucidating a whole body map ofthe human immune system will provide fundamental new insights into the pathways that regulate immunity and chronic inflammation that could aid in the design of new vaccines and immuno-therapeutic approaches. The focus of this proposal is to test whether human lymphoid versus non-lymphoid tissues are populated with phenotypically and functionally distinct innate lymphoid cells (ILCs) and to interrogate the functional significance of ILCs in maintaining tissue homeostasis in the lung and intestine. Employing flow cytometry and genome-wide transcriptional profiling, studies outlined in Aim 1 will comprehensively characterize the phenotypic and functional potential of tissue-resident ILCs isolated from the bone marrow, blood, spleen, lymph nodes, lung and intestine. To complement this analysis, we will also test whether ILCs isolated from distinct tissue sites exhibit differential responsiveness to host-derived cytokines versus microbial products. Using a novel ex vivo 3-dimensional human organoid culture system, studies in Aim 2 will test how ILCs isolated from lymphoid versus lung and intestinal barrier sites can differentially regulate epithelial cell proliferation, differentiation, barrier function and repair. Using antibody-mediated blockade approaches and chemical inhibitors, we will also test the differential contribution of different cytokine-dependent pathways in ILC-mediated regulation of epithelial function in both the lung and intestine organoid systems.